This invention relates to machines and processes for casting metal strips, slabs or bars directly from molten metal and, more particularly, for continuously casting such metal products between spaced parallel portions of a pair of revolving flexible endless metal belts which are moved along with opposite surfaces of the metal being cast, called twin-belt casting machines or twin-belt casters.
The invention is described as embodied in the structure and operation of a twin-belt continuous casting machine in which the molten metal is fed into a casting region between opposed, parallel portions of a pair of moving, flexible metal belts. The moving belts confine the molten metal between them and carry the metal along as it solidifies into a strip, slab or bar. Spaced rollers having narrow ridges support and guide the belts while holding them accurately positioned and aligned as they move along so as to produce a cast metal product of high quality and having good surface qualities. The vast quantities of heat liberated by the molten metal as it solidifies are withdrawn through the portions of the two belts which are adjacent to the metal being cast. This large amount of heat is withdrawn by cooling the reverse surfaces of the belts by means of rapidly moving, substantially continuous, films of liquid coolant traveling along against these surfaces. The edges of the molten strip are contained between a spaced, parallel pair of side dams in the form of a plurality of blocks strung together on flexible metal straps to form a pair of endless flexible assemblies suitable for containing the molten metal as it solidifies.
Examples of twin-belt casting machines will be found in U.S. Pat. Nos. 2,640,235; 2,904,860; 3,036,348; 3,041,686; 3,167,830; 3,828,841; 3,848,658; 3,878,883; and 3,864,973.
In machines of this type, the moving belts are very thin and are cooled by substantial quantities of liquid coolant, usually water containing corrosion inhibitors. This coolant serves to cool the metal from its molten state as it enters at one end of the machine causing it to solidify as it passes through the machine. As will be understood, solidification of the metal product takes place from outside to inside so that, through most of its passage through the machine, it is in the form of a solidified shell having a molten, constantly decreasing, interior volume. It will also be understood that, as the metal cools and solidifies, it shrinks. The shrinkage is very slight but, nevertheless, is sufficient to cause surface regions of the metal sometimes to pull away from the cooling, moving belts or from the side dams which serve as cooling means for the side surfaces of the product being cast. When this separation between areas of the metal surface and the cooling surface occurs, hot spots and non-uniform cooling are caused, which result in imperfections in the finished casting.
It is an object of the present invention to provide method and apparatus for continuously casting metal strip of high quality directly from molten metal.
Other objects are to provide such method and apparatus wherein the contact pressures between the casting belts and the metal strip and between the side dams and the metal strip are continuously monitored along the length of the strip to maintain and assure desired predetermined contact pressures therealong and to assure desired pressure distribution.
It is among the many advantages of the method and apparatus of the present invention that the mold contact parameters of the casting operation in a twin-belt casting machine are enabled to be more precisely controlled than previously and can be automatically controlled by a feedback system if desired.